Field of the Invention
The present invention relates to an image forming apparatus that forms an image by transferring and fixing a toner image onto a paper sheet, and an image forming system that includes an image forming apparatus.
Description of the Related Art
There have been electrophotographic image forming apparatuses such as printers and copying machines. In such an image forming apparatus, a paper sheet might be electrostatically charged during image formation or paper conveyance. When such electrostatically charged paper sheets are discharged from the apparatus and are stacked, the repulsive force or adsorptive force generated between the paper sheets might cause a problem with the stacking.
To counter such a problem, a technology involving a charging unit that electrically charges paper sheets prior to stacking has been suggested (see JP 2012-140223 A, for example).
In an image forming apparatus, a latent image formed on a photosensitive drum is visualized through development with toner, the visualized toner image is transferred from the photosensitive drum onto a transfer belt by a primary transfer process, the toner image transferred onto the transfer belt is further transferred onto a paper sheet by a secondary transfer process, and the toner image transferred onto the paper sheet is fixed onto the paper sheet. In this manner, an image is formed on the paper sheet.
The toner to be used in the image forming apparatus has wax added thereto to enhance the separability between the fixing roller and a paper sheet in the fixing unit. In the image forming apparatus, the fixing unit heats and presses the paper sheet, to fix the toner onto the paper sheet.
If the temperature of the toner on the paper sheet that has passed through the fixing unit and is being conveyed into the charging unit is higher than the crystallization temperature of the wax, the wax is melted. If the paper sheet with the melted wax is conveyed into the charging unit, the wax adheres to the charging roller electrically charged by the charging unit. Since the wax is an insulator, the wax adhering to the charging roller degrades charging performance.